/Engine/Source/Editor/UnrealEd/Public/Editor.h
Sent after the user switches between from PIE to SIE, or vice-versa. Passes in whether we are currently in SIE
static [FOnPIEEvent](API\Editor\UnrealEd\FEditorDelegates\FOnPIEEvent) OnSwitchBeginPIEAndSIE;